No need for apologies IR - it was nice you'd remembered that I'd commented on Mitchell before... as for you question about 'character' - well, that's not a question that I can answer succintly but I think it starts with the critique of the concept of essentialism that is such an important aspect of postmodern literature and theory. One of the canoncial strategies of the classic realist text is the grounding of given characters in a social mileu that is subject to certain pressures. The 'narrative' evidenced in the text is the tracking of the effects of those pressures on the given character(s) - the novel being the story of their 'development', in time, towards a certain positied sense of awareness, elightenment, self-realization etc that, once achieved, leads to an ending and a final closure. One of the pleasures of reading such works is the sense of identification the reader might feel with the character(s) - a humanistic identification with their dilemmas, situation, 'learning process' etc and it is in this encounter that the 'meaning' of a literary text is often thought to reside. However, the assumptions on which such fiction is based, the concept of the transparency of langauge, the idea of the 'sovereign' self have being exploded: the subject is fragmented, the text opaque, language and social experience, it is argued, are now constitutive of the subject and not the other way round. To rely too much on 'common sense' notions of self, identification etc is something of a cop out - it ducks all the difficult but central questions that challenge the writer. ANd that's where I think Mitchell is at: he wants his pre-modernist cake and to eat his postmodernism too: the 'meaning' of his work is too reliant on the assumptions and practices of the very thing he supposedly critiques...
(Reading this back, I'm not sure it makes much sense: you'd need to give me a couple of weeks and few thousand words, I reckon, to really try and grapple adequately with your question).
As for Calvino and If on a Winter's Night... - well, personally, I think there's more in a handful of pages of that wonderful novel than whole printed output of Mitchell (but we'll have to agree to differ there).
The Borges influence is foregrounded by Mitchell himself in Ghostwritten (which is what I meant about him making himself look an idiot: don't explicitly evoke the shadow of a master when you're nothing but a callow ingenune, it just shows your efforts in a bad light) when, I think, in one of the chapters a ghost (is it? a disembodied presence anyway) goes around inhabiting certain figures in history, one of which, Mitchell makes clear, is meant to be taken for Borges. The form of the novel - a labyrinthine structure - is clearly taken from Borges (who, really, bequeathed a whole vocabuarly of metaphors to his succesors of which the labyrinth is the most important) and, at the end of Ghostwritten, when you realize that the different chapters, narratives etc have all existed simultaneously in the mind of a man on the point of his death I think you're meant to think Ghostwritten is like the novel theorised in Borges's story 'The Garden of Forking Paths' - a novel which is just like a labyrinth, a spatial structure, in which all times, and all possibilities are made to be simultaneously present. (And probably the novel theorised in 'Tlon' too - in which only the most attentive of readers will be able to discern the true and terrible reality underlying its apparent surface).
As I say - this is all a bit haphazard and rambling, so forgive me if it doesn't make as much sense as I'd like it to ...